The present invention concerns a steering-wheel skeleton with a hub, spokes, and a rim.
Steering-wheel skeletons of this type are usually composed of several parts fastened together by rivets, screws, soldering, welding or a combination thereof and then finished by extruding plastic around them or covering them with leather or a similar material. The skeleton constitutes the supporting structure and must be designed strong enough to support the forces exerted on the steering mechanism by the driver. An increasing number of extra functions must also be taken into account when designing such a skeleton. At least both a conveniently accessible mechanism for actuating the horn and an airbag for example must be accommodated in the steering wheel. More and more switches and buttons for various vehicle functions must also be mounted directly on the wheel where the driver can operate them without having to remove his hands from it.
Finally, the steering-wheel skeleton must be designed to ensure passive safety, meaning that it must not cause severe injuries in the event of an accident. For this reason, in particular, contemporary steering wheels are more or less bowl-shaped, with the outer rim toward the driver and the hub farther forward and with the spokes accordingly slanting inward and forward toward the hub.
It should be obvious from the foregoing that all these demands can best be satisfied with a composite steering wheel, allowing all the to some extent opposing requisites to be achieved simultaneously. It is on the other hand always attempted to make manufacture costs as reasonable as possible, which is of increasing significance to traditional automobile manufacturers due to the growth in international competition. There has accordingly been no lack of attempts to construct even such complicated steering wheels of as few parts as possible. Known from U.S. Pat. No. 4,359,911 for example is a steering-wheel skeleton with a central assembly comprising a hub and spokes stamped out of sheet metal and with a separate rim enclosed by and riveted to the ends of the spokes. The central assembly and the rim can be made of different materials, allowing the specific demands made of each part to be complied with independently. Still, the fastening method is comparatively complicated.
Known from German 3 719 658 A1 is a steering wheel made of sheet metal and comprising an outer sheet-metal bowl facing the driver and a force-transmitting sheet-metal bowl fastened behind it with space left between them that comprises the rim. No radial spokes as such are involved, and the overall assembly looks like a disk when viewed head-on. This approach is intended to save weight, simplify manufacture, and improve safety in that the rear bowl can deform and tightly encloses a volume of air up to specific flow cross-sections. The bowls are fastened together air tight along their circumferences, in the vicinity of the rim, that is.
This known steering wheel consists, apart from an insert in the hub, of only two components and is accordingly relatively simple to manufacture. It is, however, not ergonomically satisfactory because the fingers cannot fit very far around the rim. Furthermore, such additional components as switches, buttons, etc. would considerably compromise its tightness. Finally, the purpose of the air-filled interior can today be attained much more effectively with an integrated airbag. An airbag, however, could not be employed in such a wheel without sacrifice to its basic concept.
There is accordingly a need for a steering wheel of the type hereinbefore described that would be even less expensive to manufacture but would not be subject to any limitations in design with respect to the aforesaid demands while still allowing the accommodation of the aforesaid additional functions.